Communication devices such as terminals are also known as e.g. User Equipments (UEs), mobile terminals, stations (STAs), wireless devices, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a wireless communications network, such as a Wireless Local Area Network (WLAN), or a cellular communications network sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via an access network and possibly one or more core networks, comprised within the wireless communications network.
The above communications devices may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The communications devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the access network, such as a Radio Access Network (RAN), with another entity, such as another communications device or a server.
The communications network covers a geographical area which is divided into geographical subareas, such as coverage areas, cells or clusters. In a cellular communications network each cell area is served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or Base Transceiver Station (BTS), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB, micro eNode B or pico base station, based on transmission power, functional capabilities and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless devices within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Institute of Electrical and Electronics Engineers (IEEE) 802.11 (IEEE Computer Society, “IEEE Std 802.11™-2012, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”, ISBN: 978-0-7381-7245-3 STDPD97218) is a set of Media Access Control (MAC) and PHYsical layer (PHY) specifications for implementing Wireless Local Area Network (WLAN) computer communication in the 2.4, 3.6, 5, and 60 GHz frequency bands. They are created and maintained by the IEEE Local Area Network (LAN)/Metropolitan Area Network (MAN) Standards Committee (IEEE 802). The base version of the standard was released in 1997, and has had subsequent amendments. The standard and amendments thereof provide a local area wireless computer networking technology that allows electronic devices to connect to a network. A WLAN is sometimes referred to as a WiFi network.
In a WiFi network, communications devices, sometimes referred to as stations (STAB), are associated to one or more Access Points (APs) in order to communicate with each other and to the Internet. Several communications devices may be within direct reach of each other, and since they share the same communication medium, i.e. the WiFi network, mechanisms to avoid collisions exist.
In for example the WiFi network in accordance with the IEEE 802.11 standard, a carrier sensing mechanism using 1-persistent slotted Carrier Sense Multiple Access (CSMA) with random back off time and with Collision Avoidance (CA) is used. Such mechanism is in this disclosure shortly referred to as a CSMA/CA and it will be described briefly below. For further details on 1-persistent slotted CSMA, reference is made to Multiple Access Protocols, Raphael Rom and Moshe Sidi (Raphael Rom and Moshe Sidi, Multiple Access Protocols: performance and analysis, New York, N.Y.: Springer-Verlag N.Y., Inc, 1990, ISBN:0-387-97253-6), and for further details on random backoff and CA reference is made to pages 221 and 230 in Next Generation Wireless LANs, Eldad Perahia and Robert Stacey (Eldad Perahia and Robert Stacey, Next Generation Wireless LANs, University Printing House, Cambridge University Press, ISBN: 978-1107016767).
The expression 1-persistent CSMA means that a communications device that finds a communications channel busy will attempt to access the channel as soon as it becomes available. That the sensing is slotted means that time, e.g. a period of time, is divided into time-slots of a specific size. The use of random back off means that instead of accessing the channel immediately when it becomes available, the communications device has to monitor the channel being idle for a back off integer number of time-slots, chosen randomly between 0 and a Contention Window (CW) value, wherein the CW value is a positive integer.
The CA infers two things. Firstly, prior to any transmission, the channel has to be sensed as idle for at least one time-slot, and secondly, when an ACK is not received, i.e., communication is failed, the communications device has to select a new random back off before attempting to sense and transmit again. In practice, there is also a Distributed InterFrame Space (DIFS), e.g. a distributed coordination function interframe space time, on top of the random back off. In modern WiFi technologies there are two types of mechanisms used simultaneously for the actual carrier sensing: physical carrier sensing and virtual carrier sensing.
In physical carrier sensing, the received energy measured in the analog front-end of the antenna may be determined. If the received energy is above a certain threshold value, the channel is regarded as occupied. Traditionally, when a communications device, e.g. a STA, detects the channel to be busy by physical carrier sensing, it continues to monitor the channel until it becomes available. This is referred to as 1-persistent carrier sensing.
Another variant of physical carrier sensing is preamble detection in which a receiver, e.g. a first communications device, actively tries to detect and decode a PHY layer preamble of a transmitter, e.g. a second communications device. Typically, the transmitter is of the same technology as the receiver. If a preamble is detected and decoded, information of the expected duration of the full communication exchange is available in the duration field of the header. IN IEEE 802.11ah, this is referred to as Response Indication Deferral (RID). For further details on physical carrier sensing, reference is made to page 228 of Next Generation Wireless LANs, Eldad Perahia and Robert Stacey (Eldad Perahia and Robert Stacey, Next Generation Wireless LANs, University Printing House, Cambridge University Press, ISBN: 978-1107016767).
Virtual carrier sensing utilizes channel reservation information carried in the MAC headers announcing imminent use of the communications medium, e.g. the WiFi network. In WiFi, the virtual carrier sensing mechanism is referred to as Network Allocation Vector (NAV), and the time extracted from the header may be referred to as the NAV time. It should be noted that the virtual carrier sensing is similar to the version of physical layer sensing wherein the preamble is decoded, but in virtual carrier sensing, higher layers than just the PHY layer has to be involved. And more importantly, in virtual carriers sensing, the whole packet needs to be decoded in order to recover the MAC header.
In wireless communications, it may be of interest to maximize the utilization of available bandwidth. For example, choosing the appropriate Modulation and Coding Scheme (MCS) optimizes the throughput. Having a robust MCS, e.g. a low communication rate, leads to high reliability, but requires more time for the communication, while a too weak MCS, e.g. a high communication rate, reduces the reliability, but enables communication in shorter time. The task of choosing the right MCS is conventionally done by an algorithm called the Minstrel algorithm. In short, the task of the Minstrel algorithm is to choose the resource, in this case the MCS, that provides the best throughput. For more details regarding the Minstrel algorithm, see https://wireless.wiki.kernel.org/en/developers/documentation/mac80211/ratecontrol/minstr el.
Long Range Low Power (LRLP) is a new topic interest group within the IEEE 802.11 working group. The intention with LRLP is to provide increased communication range as compared the communication range provided by the IEEE 802.11 ax, and to enable the use of low power communications devices running on battery. One key feature to enable the increased communication range is a narrow frequency band. Currently, the proposal is to split the total bandwidth used by the IEEE 802.11ax into a number of sub-channels, wherein each sub-channel may be used as a full channel for a narrow band LRLP communications device. Thus, the LRLP communications devices may interact on the same band as the legacy IEEE 802.11 communications devices. The bandwidth of LRLP communications devices and total number of sub-channels have not yet been agreed upon in the IEEE 802.11 standardization, but preliminary discussions suggest that there may be from 4 to 9 sub-channels per 20 MHz. Thus, the sub-channel bandwidth may be around 2 MHz to 5 MHz.
For LRLP communications devices, low power is a main focus. Sampling a large channel bandwidth requires power, and therefore, an LRLP communications device may not have the capability to sample the full bandwidth over which the IEEE 802.11ax WiFi is operating. Instead, the LRLP communications device may only be able to sample one sub-channel at a time. Currently, the LRLP idea to resolve this is to let the AP schedule the use of the channel for the LRLP communications devices. For example, the AP may transmit a legacy preamble, occupying the channel so that the legacy communications devices may back off for a certain period of time. After this is done, there may be several modes of LRLP operation. For example, one mode of LRLP operation may be a scheduled mode, wherein the AP schedules each LRLP communication device to a certain sub-channel and period of time in order to maximize some utilization criteria. Another example of a mode of LRLP operation is a non-scheduled mode, wherein the LRLP communications devices compete for the media under a predefined time.
One wide-spread technology using multiple non overlapping sub-bands is Bluetooth. However, Bluetooth does not perform any carrier sensing. Instead, it uses a Frequency Hopping Spread Spectrum (FHSS) technique, which switches among sub-channels and uses them immediately without any sensing. A collision on one sub-channel is resolved at higher layers, for example by retransmission. The switching among sub-channels follows a pseudorandom pattern known to both the transmitter and the receiver. If a certain sub-channel turns out to often be bad, it may be blacklisted by the transmitter. The blacklist needs to be known also to the receiver. When a sub-channel on the black list is selected, the transmitter refrains from using that sub-channel and instead moves on to the next good sub-channel.
In the document Single-radio multi-subchannel random access for OFDMA wireless networks, to Jia Xu, Pin Lv and Xudong Wang (Jia Xu, Pin Lv and Xudong Wang, “Single-radio multi-subchannel random access for OFDMA wireless networks, “Electronics Letters, 49(24) pp. 1574-1575, November 2013), CSMA over multiple sub-channels is considered. Further, full sampling over all sub-channels is available, and several sub-channels are used for data transmission.
Some drawbacks with the existing solutions for utilization of multiple sub-channels is that they are either scheduled as in 3GPP-like communication schemes; that they are blindly transmitting on sub-channels as in Bluetooth, or that they require the capability to monitor all the sub-channels simultaneously,